Thomson, William (Lord Kelvin) (1824–1907)

Scottish theoretical and experimental physicist, born in Ireland, who proposed
the thermodynamic temperature scale
(1848), now measured in kelvin, and inferred
the so-called heat death of the universe
based on an extrapolation of the second
law of thermodynamics (heat cannot flow spontaneously from a cooler
object to a hotter one).

Thomson estimated the age of Earth by calculating how long it would take
for an Earth-sized ball of rock to cool from its initial molten state. His
value – 20 to 400 million years – was much too low because he
knew nothing about the heat still being generated inside our planet by radioactive
decay. He also estimated the Sun's age, based on the most efficient energy
source he could imagine, which was the slow release of gravitational energy
by contraction (see Kelvin-Helmholtz
contraction). Again, he had no way of knowing that, in nuclear
fusion, there is a vastly more potent way of generating heat and light.

Thomson and Michael Faraday's work on electromagnetism
gave rise to the theory of the electromagnetic field, and his papers, with
those of Faraday, strongly influenced James Clerk Maxwell's
work on the electromagnetic theory of light (though Thomson himself rejected
Maxwell's abstract theory). His work on wire-telegraphic signaling played
an essential part in the successful laying of the first Atlantic cable.

Quote by Thomson

"I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meagre and unsatisfactory kind."

– from Popular
Lectures and Addresses

Thomson and panspermia

In his 1871 presidential address to the British Association for the Advancement
of Science,1 Thomson surprised the scientific community by declaring
his support for a version of the theory of panspermia:

Should the time come when this earth comes into
collision with another body, comparable in dimensions to itself ... many
great and small fragments carrying seeds of living plants and animals
would undoubtedly be scattered through space. Hence, and because we all
confidently believe that there are at present, and have been from time
immemorial, many worlds of life besides our own, we must regard it as
probable in the highest degree that there are countless seed-bearing meteoric
stones moving about through space. If at the present instance no life
existed upon this earth, one such stone falling upon it might, by what
we blindly call natural causes, lead to its becoming covered with
vegetation.

Witty and derisive replies were not slow in coming. That arch-supporter
of Darwinism, Thomas Huxley (who ironically
had introduced Thomson to the BAAS meeting) wrote in a private letter: "What
do you think of Thomson's 'creation by cockshy' – God almighty sitting
like an idle boy at the seaside and shying aerolites (with germs), mostly
missing, but sometimes hitting a planet!" Thomson, however, continued to
argue his case, even urging that he considered it "not in any degree antagonistic
to ... Christian belief." Zöllner's
attack on Thomson's thesis prompted a rebuttal from Helmholtz,
who had independently put forward a similar theory of panspermia. In recent
years, with the discovery of meteorites that have
come from Mars, the concept of microbes hitching a ride from one world
to another aboard impact fragments has become scientifically respectable
(see ballistic panspermia).

Reference

Thomson, W. "Presidential Address to the British Association for the
Advancement of Science," Nature, 4, 262 (1871).